Method for operating an image sensor having an integration period uncoordinated with its frame period

Abstract

A CCD image sensor is operated in an asynchronous mode to enable it to capture short lived events, or to freeze rapid motion. The image is acquired during an integration period which is triggered by a strobe pulse, and the resulting charge is held in a storage section of the CCD sensor until a regularly occuring field read-out period, during which the charge is read-out to constitute a video signal.

I CLAIM: 
     
       1. A method of operating a CCD image sensor which includes an image section comprising a photo-sensitive portion of an array of CCD channels, a store section comprising a non photo-sensitive portion of an array of CCD channels, a line read-out section adjacent to the store section., a control electrode structure associated with said image, store, and read out sections; a charge sink structure; the control electrode structure being adapted to receive potentials which transfer charge generated in the image section into the store section, and to read out charge stored in said store section via said read-out section to provide an output video signal: the method including the steps of generating charge at said photo-sensitive portion during an integration period which is short relative to the frame period of the sensor and which occurs at an un-predetermined time with respect thereto; transferring the charge generated during the integration period into said store section at the end of said integration period; holding said charge at said store section until the commencement of a regularly occurring frame period; and reading the charge from the store section via said read-out section for the duration of said frame period so as to thereby constitute an output video signal. 
     
     
       2. A method as claimed in claim 1 and wherein the occurence of the integration period is determined by an externally applied strobe signal 
     
     
       3. A method as claimed in claim 2, and wherein the duration of the strobe signal determines the duration of the integration period 
     
     
       4. A method as claimed in claim 1, and wherein regular charge clearance of the image section occurs prior to the application of the strobe signal 
     
     
       5. A method as claimed in claim 1, and wherein charge clearance of the image section is initiated by the application of the strobe signal, this charge clearance period being shorter than the following integration period. 
     
     
       6. A method as claimed in claim 2, and wherein regular charge clearance of the image section occurs prior to the application of the strobe signal. 
     
     
       7. A method as claimed in claim 2, and wherein charge clearance of the image section is initiated by the application of the strobe signal, this charge clearance period being shorter than the following integration period. 
     
     
       8. In a method of operating a CCD image sensor having a frame period and which includes an image section comprising a photo-sensitive portion of an array of CCD channels; a store section comprising a non-photo-sensitive portion of an array of CCD channels; a line read-out section adjacent to the store section; an electrode structure for controlling operation of the image section, the store section, and the line read-out section; and a charge sink structure, the electrode structure being responsive to an applied voltage to cause charge generated in the image section to be transferred to the store section and to read out charge stored in the store section via the read-out section to produce an output video signal, the steps comprising: clearing charge from the image section until a trigger pulse is received by the electrode structure, the trigger pulse being relatively short compared to the frame period and uncoordinated with the frame period;   generating charge at the image section in response to incident radiation while the trigger pulse is maintained;   transferring generated charge from the image section to the store section when the trigger pulse ends;   holding the generated charge at the store section until the commencement of another frame period; and   reading out the generated charge from the store section via the read-out section as an output video signal.